The project, announced by Putin during a December 2014 visit to Turkey, will carry gas from Russia under the Black Sea to Turkish Thrace. One line, with a 15.75 billion cubic meters capacity, is expected to supply the Turkish market with a second carrying gas to Europe.
Negotiations over the pipeline were halted after Turkey shot down a Russian jet over the Turkey-Syria border in November 2015 but have since been resumed.
In September, Gazprom said construction could start by the end of 2017 if an intergovernmental agreement was signed in October, with the goal of completing the pipeline by 2019.
Turkey, which is the second biggest consumer of Russian gas after Germany, imports around 30 billion cubic meters of gas from Russia annually via two pipelines - the Blue Stream, which passes under the eastern Black Sea, and the Western Line through the Balkans.
It is hoped the new pipeline will bring gas price discounts for Turkish customers. Under current agreements between the Turkish BOTAŞ pipeline corporation and Gazprom, both sides have the right to ask for price revisions.